1. Field
This disclosure relates generally to semiconductor devices, and more specifically, to dual gate oxide device integration.
2. Related Art
In many instances, dual gate oxide (DGO) devices need to be integrated on the same substrate. As used herein, the term dual gate oxide devices relates to devices that are formed on the same substrate, but have different gate oxide thicknesses. For example, thicker gate oxide devices may be formed on the periphery of the substrate so that they can handle higher voltages associated with input/output operations. Thinner gate oxide devices may be formed in areas of the substrate where higher voltages are not present. Metal gate with high dielectric constant (high k) devices increasingly need materials that may not be compatible with existing methods for forming dual gate oxide devices. For example, such metal gate/high k dielectric devices may need silicon germanium channels to lower the threshold voltage (Vt) associated with the PMOS devices. Conventional processes, such as thermal oxidation, used to form thick gate oxide devices, however, are not compatible with silicon germanium channels. This is because if thick gate oxide is grown over silicon germanium, the thermal oxidation step results in the germanium diffusing into the regions of the substrate or the gate oxide that should not contain any germanium. In sum, thermal oxidation step used as part of the conventional dual gate oxide integration process may degrade the profile of the silicon germanium channel.
Accordingly, there is a need for improved dual gate oxide device integration.